Such lamps have a discharge vessel filled with a discharge medium, for example, a noble gas—with or without the addition of mercury and any other additional fillings. Two electrodes are arranged facing each other inside the discharge vessel. Two piston shafts are arranged on the discharge vessel, via which current feed elements are fed in a gastight manner to the outside for electric contact. For lamp types operated with direct current, the anode is usually designed with an electrode head with high thermal resistance, in which the radiated heat power is optimized by adequate dimensioning. In contrast, the electrode on the cathode side is designed with a comparatively small, conical electrode head.
High-pressure discharge lamps which emit UV radiation are used for the patterning (lithography) of semiconductors. Suitable mercury vapor short-arc discharge lamps from OSRAM are sold under the product name HBO®. To increase productivity, the semiconductor industry requires powerful discharge lamps which emit UV radiation in the region of the mercury i-line at 365 nm. In operation such discharge lamps may not as a rule exceed a line width (FWHM) of approx. 2.5 nm, so that to increase the radiation intensity the mercury density of the filling cannot simply be increased. This in turn means that the lamp voltage applied to the electrodes cannot be significantly increased either.
One possibility for significantly increasing the radiated power is therefore to increase the lamp current and thereby the electric power for connection purposes. In particular, in the case of HBO IC lamps and an effective supply current of more than 220 A, the sealing elements (e.g. sealing films) become very warm (Joule heat loss). An effort is made to reduce the thermal load of the large anode by diverting part of the heat via the current feed and the supply line on the anode side.
The electrodes are each connected to the respective supply lines via an electrode rod, several molybdenum sealing films and an outer current feed which penetrates the piston shaft on the front side, as a rule the supply on the anode side being via a flexible supply line which extends from the lamp axis in an approximately radial direction. The contact on the cathode side is as a rule via a base pin which projects from the base on the cathode side.
In particular, the base on the anode side requires efficient cooling in the case of high-wattage, high-pressure discharge lamps with currents of more than 220 A because as a result of the Joule heat of the sealing films and as a result of the heat conducted by the electrode and also as a result of the heat radiation in a lamp housing (e.g. with lithography use) possibly reflected back, it is heated very intensely. The outer current feed components, which are in direct contact with the ambient atmosphere, can in this case oxidize at temperatures of more than 300° C. during operation of the lamp and then lead to the failure of the discharge lamp.
To improve cooling a solution is shown in WO 2007/000141 A1 in which the base is designed with cooling fins on the anode side in order to expand the heat exchange surface. With such a solution, there is also the problem that the thermal contact between the base and the outer current feed is only made indirectly by welding the supply line to the outer current feed on the one hand and to the base on the other hand. I.e. the section of the supply line between the outer current feed and base wall represents a kind of heat bridge, the size of which on account of the length of the supply line between power supply and base peripheral wall and the small supply cross-section is too small, however, to ensure adequate heat dissipation from the outer current feed to the base. I.e. even in the case of a base with heat fins, on account of the poor thermal contact between outer current feed and base, overheating is not ruled out.